Title : Environmental impacts of shale gas extraction: example of northeastern British Columbia, Canada
Abstract:
Oil and gas well leakage is of public concern primarily due to the perceived risks of aquifer contamination and greenhouse gas (GHG) emissions. This study examined well leakage data from the British Columbia Oil and Gas Commission (BC OGC) to identify leakage pathways and initially quantify incident rates of leakage and GHG emissions from leaking wells. Three (3) types of leakage are distinguished: “surface casing vent flow” (SCVF), “outside the surface casing leakage” (OSCL) and “cap leakage” (CL). In BC, the majority of reported incidents involve SCVF of gases, which do not pose a risk of aquifer contamination but do contribute to GHG emissions. Reported liquid leakage of brines and hydrocarbons is rarer. OSCL and CL of gas are more serious problems, due to the risk of long-term leakage from abandoned wells; some were reported to be leaking gas several decades after they were permanently abandoned. According to the requirements of provincial regulation, 21,525 have been tested for leakage. In total, 2,329 wells in BC have had reported leakage during the lifetime of the well. This represents 10.8% of all wells in the assumed test population. However it seems likely that wells drilled and/or abandoned before 2010 have un-reported leakage. In BC, the total GHG emission from gas SCVF is estimated to reach about 75,000 metric tonnes per year based on the existing inventory calculation; however, this number is likely higher due to underreporting.
